Transformers and impedanceHow do you turn 110 volts into 55?

A transformer converts an alternating voltage at one level to an alternating voltage at a higher or lower level (step up or step down). It uses mutual induction. A continually changing flux in the primary winding induces a voltage in the secondary winding. That's why a transformer only works on AC: DC doesn't produce a changing flux.

V₁ / V₂ = N₁ / N₂
110 / V₂ = 50 / 25   →   V₂ = 55 V

• Fewer turns on the secondary means step down, and more turns means step up. You can tell which one a transformer is by comparing the windings.
• On drawings, the primary is usually on the left and the secondary on the right.
• The two coils never touch. The voltage is induced across through the magnetic field in the core.
• The core is laminated (thin lacquered layers) to reduce losses.

Types you'll see: step-up, step-down and isolating transformers. An isolating transformer separates you from earth, so there's no path through your body to earth. A bathroom shaver socket has one inside. You'll also see pole-mounted three-phase transformers, current transformers (CTs), potential transformers, and the big fenced-off "Danger, high voltage" substations near housing estates.